The automation of industrial sites implies major safety considerations. AS-i (Actuator Sensor Interface) Safety, for example, the safety-oriented extension of AS-Interface, facilitates the standard operation of standard and safety sensor technology in a joint bus connection that has all the well-known system advantages of AS-Interface. Since the year 2000 AS-i Safety has been certified as a reliable bus system for applications up to Category 4(EN 954-1) by the TÜV-Nord of the Berufsgenossenschaftliches Institut für Arbeitssicherheit.
Normally, for example when a gate is monitored in a safety system, a sensor for generating a signal for at least two positions is connected to a bus and the status of the sensor (open gate, closed gate) is evaluated, and if there are no errors, the sensor generates a message that it is in correct position.
FIG. 5 illustrates a safety monitoring system 550 comprising: a common bus 551, such as AS-i bus, a controller 552 comprising a power supply and a driver/master, and number of monitored devices and sensors (not all illustrated), such as non-contact sensors 553, interlocking devices, magnetic switches, stops 554, emergency grab wire switch with dual switching, three-position devices, relays 555, two-hand control devices 556, foot operated switches 557, safety contact rails, bumpers, mats, fencing system, safety roller doors, etc.
WO 03/093999 discloses an inherently fail-safe processing, having two processing units: a first processing unit with a first data processor and/or controller; at least one input port for input data received from at least one remote unit; at least one output port for output data to be transmitted to at least one remote unit. The first processing unit comprises means for generating a unique code for functional control of the processing and/or receiving and/or transmitting steps being performed and a port for the transmission of the generated check-words. A functional checker and protection unit is provided, which consists of a second inherently fail-safe processing unit, which executes a program for checking the functional steps of the first processing unit and a program for checking the correctness of functional control codes and the time sequence thereof. The checker and protection unit communicates with the first processing unit and generates signals for enabling it when check-words are correct, and signals for disabling the first processing unit and/or for forcing the transmission of predetermined output data for fail-safe remote unit control, or generates itself predetermined output data for fail-safe remote unit control and/or enables/disables vital functions of the remote unit and/or of the first processing unit.